VERTICAL DIPOLE FOR 40M (AND HIGHER)

LIGHTWEIGHT PORTABLE VERTICAL DIPOLE ON A FIBREGLASS FISHING POLE

An advertisement for the i-Pole by Proantennas on the WIMO Homepage made me curious and I decided to give that antenna system a try too. My primary interest was a lightweight portable vertical antenna for 40m, as for 20m - 10m I use my C-Poles.

Many thanks to Steffen, DL6SFR, for sending me two more links to portable vertical dipoles (see bottom of page).

A load of telescopic whips I bought at a Radio Shack Sale on a recent trip to the US, as well as a 6m / 0.6m fibreglass pole from Lambdahalbe awaited to be used in a project. Unfortunately at the time of writing the telescopic whips are no longer avalable at Radio Shack, but any whip could be used.

4 telescopic whips per capacity hat, total span 1.9m, mounted crosswise bottom to bottom on angle brackets of different sizes to fit the pole

I chose the distance between the two capacity hats for a resonance at 20m without loading coils:

As I mentioned before, my interest was mainly a vertical dipole for 40 m. So I opened my EZNEC 5+ and started to model. The distance between the capacity hats of 4.3 m was given by the 20m resonance. Because of the asymmetric ground load at the lower leg of the antenna, I fed the dipole silightly off center and reduced the inductance of the lower loading coil empirically.

The loading coils were wound on a 50mm PVC tube. 13 and 14 turns of installation wire and the shorted stub from the EZNEC simulation was substituted by an airwound coil across the feedpoint of 11 turns with16 mm inner diameter.

That's how the first setup of the coil assembly looked like. (Note that the coil was mounted upside down on this photo. The coax shield and the lower inductance should be towards ground).